Light, moisture and nutrients are factors which determine the yield of seed crops. Water absorbing chemicals have been used as coatings on seeds or broadcast onto and into the soil. Water absorbent chemicals attract moisture to the seed to provide earlier germination, more uniform stands and increased yields.
In particular, starch graft polymer compositions absorb and retain under pressure large quantities of fluids. In U.S. Pat. Nos. 3,997,484, 3,935,099 and 3,985,616 to Weaver et al, starch graft polymers are described which have the ability to absorb very large amounts of water equalling up to more than 1,000 times their own weight.
Many variations of starch graft copolymers are available on the market and have been applied as coatings on substrates, such as seeds, to increase the water holding capacity of the substrate.
Seeds have been coated with herbicides, fungicides or super absorbents, such as the family of super water absorbents sold under the trademarks SORBEX 200 and SGP (for Starch Graft Polymers) by the Henkel Corporation. Seeds have been coated by feeding the powder onto seeds rotating in a cement mixer. Liquids have also been sprayed onto seeds to provide a coating of a desirable chemical.
All plants require a variety of nutrients and trace elements or micronutrients. It is known that many bacteria may form a beneficial association with plants. Bacteria of the genus Rhizobium infect the roots of legume plants, such as clover, alfalfa and beans. The roots respond to these infections by producing lump-like growths or nodules in which the bacteria grow. The bacteria incorporate free nitrogen, some of which is made available to the host plant.
While the addition of bacteria to seeds has been recognized as beneficial to increasing crop yields, bacteria die quickly in dry soils. Bacteria, if applied to seeds, must be maintained in a dormant state until planted and must be activated only when conditions favor optimum growth.